1. Field of the Invention
This invention relates to a new control system for a gas furnace and to a new control device for such a system as well as to new methods of making such a control system and such a control device.
2. Prior Art Statement
It is known to provide a control system for a gas furnace wherein the system comprises a pilot burner means, a main burner means, and an electrical circuit means, the circuit means comprising an electrically operable pilot gas valve means, an electrically operable main gas valve means, an igniter means for generating sparks to ignite fuel issuing from the pilot burner means, a transformer means operatively associated with the igniter means for generating the sparks therewith, flame sensing means operatively associated with the pilot burner means for sensing flame at the pilot burner means through flame rectification, a thermostatic switch means, and control means operatively associated with all of the means to cause the pilot valve means to issue gas from the pilot burner means and to cause the transformer means to create igniting sparks with the igniter means when the thermostatic switch means determines that the furnace should be in an "on" condition, the control means thereafter causing the main valve means to issue gas from the main burner means and to cause the transformer means to cease generating the sparks when the flame sensing means senses flame at the pilot burner means, the circuit means comprising a frame ground that is also the circuit ground for the circuit means, the transformer means comprising a secondary winding having a first end thereof electrically interconnected to the igniter means and having a second end thereof interconnected to the frame ground. For example, see the control system that uses the control device sold as the SP-715 control device by the Simicon Division of the Robertshaw Controls Company, Holland, Mich. Also, see the U.S. patents to Geary, U.S. Pat. Nos. 4,865,539 and 4,915,614 for similar systems.
It is also known to interconnect the second end of the secondary winding of the transformer means of such a system to a frame ground with a gas breakover device and separate the frame ground from the circuit ground with a resistor so that two separate grounds are provided for the system. In this manner, the same probe for the igniter means can be used as the flame sense probe.